Microstructural Evolution During Solution Treatment of ADC12 (A383) Alloy Die Castings

Abstract

High-pressure die casting (HPDC) components are known to be not heat treatable due to the formation of unacceptable surface blisters, dimensional instability, and poor mechanical properties during conventional solution treatment, such as at 540°C for 8 h. In the present study, the possibility of solution treating a recycled ALDC12 HPDC alloy at temperatures less than 500°C and with shorter solution treatment times was investigated. HPDCs with thickness of 2 and 3 mm were solution treated at 490°C for various times ranging from 15 to 180 min. Microstructural evolution during solution treatment was examined by various techniques, including metallography, energy dispersive spectrometry, electrical conductivity, and X-ray diffraction. Results indicated that almost all of the Al2Cu intermetallics were dissolved within 90 min of solution treatment. The coarsening of eutectic Si particles was found to follow the Lifshitz–Slyozov–Wagner theory with two distinct regimes. Furthermore, measurements of Cu concentration within α-Al dendrites revealed that the diffusion of Cu atoms in α-Al phase is not the primary limiting factor for homogenization of the alloy. Most importantly, no blisters were observed at the surface of the castings. Therefore, this heat treatment can be used for HPDC components from ALDC12 alloy at a reasonable time.